linux-kernel - Re: [PATCH] drm/msm/adreno: fix gpu probe if no interconnect-names

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Date:   Wed, 15 Jul 2020 11:46:55 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Jonathan Marek <jonathan@...ek.ca>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Brian Masney <masneyb@...tation.org>,
        John Stultz <john.stultz@...aro.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <freedreno@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/adreno: fix gpu probe if no interconnect-names

On Wed, Jul 15, 2020 at 11:37 AM Jonathan Marek <jonathan@...ek.ca> wrote:
>
> On 7/15/20 2:29 PM, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > If there is no interconnect-names, but there is an interconnects
> > property, then of_icc_get(dev, "gfx-mem"); would return an error
> > rather than NULL.
> >
> > Also, if there is no interconnect-names property, there will never
> > be a ocmem path.  But of_icc_get(dev, "ocmem") would return -EINVAL
> > instead of -ENODATA.  Just don't bother trying in this case.
> >
> > Fixes: 8e29fb37b301 ("drm/msm: handle for EPROBE_DEFER for of_icc_get")
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >   drivers/gpu/drm/msm/adreno/adreno_gpu.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > index 0527e85184e1..c4ac998b90c8 100644
> > --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > @@ -979,6 +979,7 @@ int adreno_gpu_init(struct drm_device *drm, struct platform_device *pdev,
> >       struct adreno_platform_config *config = dev->platform_data;
> >       struct msm_gpu_config adreno_gpu_config  = { 0 };
> >       struct msm_gpu *gpu = &adreno_gpu->base;
> > +     bool has_interconnect_names = true;
> >       int ret;
> >
> >       adreno_gpu->funcs = funcs;
> > @@ -1005,12 +1006,13 @@ int adreno_gpu_init(struct drm_device *drm, struct platform_device *pdev,
> >
> >       /* Check for an interconnect path for the bus */
> >       gpu->icc_path = of_icc_get(dev, "gfx-mem");
> > -     if (!gpu->icc_path) {
> > +     if (IS_ERR_OR_NULL(gpu->icc_path)) {
> >               /*
> >                * Keep compatbility with device trees that don't have an
> >                * interconnect-names property.
> >                */
> >               gpu->icc_path = of_icc_get(dev, NULL);
>
> This is misleading because if it gets a EPROBE_DEFER error (or any other
> error), it will hit this path. Maybe there's a specific error you can
> check for instead to identify the "no-interconnect-names" case?

good point, we should probably instead just explicitly check with
of_find_property("interconnect-names")

fwiw, of_icc_get() returns:

  - NULL if icc disabled, or no "interconnects" property
  - -EINVAL if name!=NULL and no "interconnect-names"
  - and looks like -ENODATA if name!=NULL but no match in
    interconnect-names

The specific error returns aren't really called out in the API comment
block, so not really sure how much we should rely on them not being
implementation details.

BR,
-R

> Also don't think its a good idea to be calling of_icc_get(dev, NULL)
> again when there's a EPROBE_DEFER, the interconnect driver could come up
> between the two calls
>
> > +             has_interconnect_names = false;
> >       }
> >       if (IS_ERR(gpu->icc_path)) {
> >               ret = PTR_ERR(gpu->icc_path);
> > @@ -1018,7 +1020,9 @@ int adreno_gpu_init(struct drm_device *drm, struct platform_device *pdev,
> >               return ret;
> >       }
> >
> > -     gpu->ocmem_icc_path = of_icc_get(dev, "ocmem");
> > +     if (has_interconnect_names)
> > +             gpu->ocmem_icc_path = of_icc_get(dev, "ocmem");
> > +
> >       if (IS_ERR(gpu->ocmem_icc_path)) {
> >               ret = PTR_ERR(gpu->ocmem_icc_path);
> >               gpu->ocmem_icc_path = NULL;
> >